【作者】 刘向阳；

【导师】 廖桂生；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2010， 博士

【摘要】 机载多通道SAR-GMTI系统不仅可以检测主瓣杂波谱带外的快速目标,还可以利用多通道技术检测主瓣杂波谱带内的慢速目标,同时实现了对动目标的参数估计和重聚焦,并精确定位在高分辨的SAR图像上,为全天时、全天候的战略和战场高分辨侦察提供了可能性,受到了世界各军事强国的普遍关注。为了检测主瓣杂波谱带内的慢速目标,该系统可以利用DPCA、ATI或STAP等多通道技术来抑制杂波,但这些技术对通道间的频率响应、回波时延、空间位置、天线空域响应等的一致性要求较高,实际系统很难满足很高的一致性要求,各种不一致性误差导致了系统性能的下降甚至恶化,如何有效的补偿这些误差成为提高系统性能迫在眉睫的难题。在某研究所实验项目的资助下,紧密结合工程实际,利用理论分析、公式推导和数据验证等手段对机载多通道SAR-GMTI系统中的误差及其补偿方法进行了研究,取得了一些成果,主要概括为：(1)论文从杂波模型出发,推导了回波的相关性与频率响应误差、回波时延误差、通道位置误差和天线空域响应误差的关系,研究了这些误差的成因及在回波数据域的补偿方法,提高了多通道SAR-GMTI系统的动目标检测性能。(2)针对通道频率响应误差导致杂波抑制性能下降的问题,根据机载多通道下视雷达地杂波数据的相关特性,提出了一种不需要校正信号的、基于回波数据的自适应盲通道均衡方法。该方法不仅可以估计并补偿通道间的频率响应误差,而且也同时补偿了回波和接收机的时延误差。(3)在补偿水平位置误差时,为了减小主瓣杂波谱带外的动目标信号的损失,提出了利用全通的时延滤波器补偿该误差的方法,同时重点分析了补偿后运动目标信号的相消特性。理论分析和实验表明,目标的相消特性不仅与通道间距、载机速度和波长有关,还取决于雷达的脉冲重复频率,因此优化脉冲重复频率的选择对解决盲速问题也是十分重要的。(4)当样本中存在强的运动目标时,自适应杂波抑制性能下降的同时也造成了动目标信号的相消。针对此问题,基于最大信噪比准则,提出了一种稳健的两通道自适应DPCA杂波抑制方法。该方法对自适应权的幅度和相位分开估计,避免了二者之间的相互影响。(5)多点消一点和联合像素方法都充分利用参考像素周围的信息,补偿了各种系统误差,有效地抑制了地杂波。研究了多点消一点和联合像素这两种稳健的杂波抑制方法的关系,实测数据结果表明,联合像素方法虽然利用了更多的信息,但如果不能有效的对动目标信号进行约束,其动目标检测性能反而低于多点消一点方法。更多还原

【Abstract】 The multi-channel airborne SAR-GMTI systems can detect not only fast moving targets outside the mainlobe clutter spectrum but also slowly moving targets inside using the multi-channel techniques. Simultaneously, the velocity of the moving targets can be evaluated accurately, and the targets can be refocused and relocated accurately on the high definition SAR image. Consequently, it makes all day/night, all-weather, strategic and battlefield reconnaissance be possible, and has caused considerable concern by all the military powers in the world. To detect the slowly moving targets inside the mainlobe clutter spectrum, the multi-channel techniques, such as DPCA, ATI, STAP, etc, can be used for clutter suppression, but they require that the frequency response between channels, time-delay of the returns, space position, airspace response of the antennas, etc, must be matched highly. In actual systems, the mismatch of these is inevitable and causes degradation of the detection performance of the system, even deterioration. Therefore, how to compensate these errors becomes an extremely urgent problem for the improvement of the system performance.Supported by the experiment project of an institute, we combine with the engineering practice tightly and carry out researches into error compensation for the multi-channel airborne SAR-GMTI systems by means of theory analysis, formula derivation and real data validation. Several key achievements are obtained and mainly summarized as:(1) Firstly, the clutter model with all the errors is derived out, and the relationship between the correlation characteristic of the clutter in the channels and the frequency response error, time-delay error of the return, space position error and airspace response error of the antennas is analyzed. Then the origin of these errors and the compensation approaches in the data field is studied in the doctoral dissertation, which greatly raise the detection performance for the moving targets in the multi-channel SAR-GMTI system.(2) To deal with the problem that the frequency response error degrades the performance for clutter suppression, an adaptive blind channel equalization method based on the echo signal is presented according to the characteristic the ground clutter for down-looking multi-channel airborne radars, in which the calibration signals is not needed. It can evaluate and compensate not only the frequency response error between channels, but also the time-delay errors induced by the receivers and returns.(3) When compensating for the azimuth position error, an all-pass time-delay filters is used to reduce the loss of the target signal outside the mainlobe clutter spectrum, and the cancellation characteristic about the target signal after compensation is analyzed in emphasis. Theory analysis and experiments show, the cancellation curve of the moving targets is related to not only the distance between channels, aircraft’s velocity and wavelength, but also the pulse repetition frequency (PRF). As a result, the optimized selection for the PRF is important to solve the problem of blind velocity.(4) While strong scattering moving targets exist in samples, the performance of adaptive clutter suppression is degraded greatly and the signal of moving targets is cancelled. To deal with this problem, a robust dual-channel adaptive DPCA method for clutter suppression is proposed based on the criterion of maximum signal-to-noise ratio. In this method, the amplitude and phase for the adaptive weight is evaluated separatedly, which avoid the influence on each other.(5) For the multi-point minus one-point and joint pixel methods, the information on the adjacent pixels associated with the reference pixel is sufficiently used for suppressing the clutter, which can compensate all the system errors effectively at the same time. The relationship with them is derived out and the performance is compared by the measured data, which shows that although more information is used for the joint pixel method, the detection performance for the moving targets is worse than that for the multi-point minus one-point method if the signal of the moving targets cannot be constrained effectively.更多还原